Digital camera with viewfinder designed for improved depth of field photographing

ABSTRACT

The present invention aims at depth or field improvements or digital cameras, where differently-focused images of a scene, to be photographed, are exposed. A final image is produced from these primary-shots, where depth of field-limitations related to classic photo-lenses, are essentially eliminated. Specific new problems related to camera-viewfinders and camera-focusing are emerging however, due to the increasing number of images being registered. Following the present invention, advantageous procedures regarding camera viewfinders, for visualizing the individual primary shots as well as images processed for improved depth of field, are outlined. A simple technique for upgrading a standard digital camera for depth of field-improvement operation, including an adequate method for preselecting focuses, is illustrated by FIG.  5 . These problems and others, related to a photographers adjustments and handling of various kinds of depth of field-enhancing cameras are remedied by applying the present invention.

BACKGROUND OF THE INVENTION

A depth of field-improving system where differently focused photographicimages of one and the same scene are being registered thereaftercombined, is known from a previous patent PCT/SE01/02889. Digitalregistration in particular, makes it feasible to obtain picturesfeaturing sharp definition from extreme proximity distance up toinfinity, more or less. Other options, referring to the same patent, aredescribed as well. Its possible, according to the same invention, toexecute separate exposures, one after another, with intervening rangeadjustments of the camera lens. However, practical circumstances make itmore advantageous in certain cases to perform these exposuressimultaneously, for example by using beamsplitters.

PRIOR ART AND ADJACENT TECHNIQUES

Cameras with viewfinders, intended for image registration on durablemedia (thus pictures of considerably longer life span than at real-timepresentation) and with a dedicated depth of field-improvement function,thus involving image processing of differently-focused images andprogrammed automatic setting of focal ranges (i.e. preselected states offocus) during the process of exposure, seem to constitute a novel art.

The problem of improving a cameras depth of field is however as old asthe camera itself and different methods have been suggested:

U.S. Pat. No. 5,307,170 is describing a video camera which registersdifferently-focused images by means of a periodically vibrating imagesensor, using some segmental- or filter method (cf PCT/SE01/02889) forextraction of high frequency image information from such image-cycles,for synthesis to resultant images with extended depth of field.

Measurement of image resolution is, as far as can be gathered from thedescription, performed by means of some kind of Autofocus (AF)procedure. The whole arrangement is described as a Video-camera withimproved Auto-Focus and ability to catch up with fast moving objects. Anautomatic movement detection function, by means of which intruders canbe automatically detected, is furthermore described and it's outlinedhow a mobile robot may thus detect and avoid obstacles. The method cantherefore, according to the patent, be used for separation of mobileobjects from its background. The course of events may be followed on animage monitor screen. The applications cited are apparently restrictedto video camera homing of fast missiles, where the normal Autofocusfunction is too slow, plus automatic detection of intruders. Alternativemethods for extracting image information from differently focused imagesare known from the other above-mentioned patent (PCT/SE10/02889),however this selective process may not necessarily be associated withhigh frequency image information (extensive image parts may almost lacksuch information) but rather by using other image information like someoptimal similarity vs a comparison- or template image, produced by othermeans. This other technique may for example consist of (at least) onesingle exposure executed with very high F-number (Like F/32), thus animage registered with considerable depth of field. The amount of lightexposed, will be very much reduced with such a small aperture, whichhowever may be compensated for, by using longer exposure time and byincreasing sensor sensitivity. The exposure time may only be extended upto a certain limit (say 1/15 second) using free hand photography ofscenes with mobile objects, while the sensitivity may be increased tosuch an extent that pictures become so noisy, i.e. ‘grainy’, that theresult may not reach the standard for an acceptable photo, howevernevertheless suffice as template picture, following the above-mentionedtechnique, and this procedure is also applicable when merging severalexposures at reduced aperture. The above-mentioned template method isalso suitable for iterative procedures including successive improvementof templates, produced by means of various techniques. Picturesregistered in wide-angle mode, i.e. with reduced focal length and largerfield of view, is providing another alternative technique (partlydescribed in U.S. Pat. No. 5,920,657). Such pictures may then, byelectronic means (electronic zoom) be enlarged to the same format andfield of view, as another picture registered at longer (telephoto) focaldistance. This enlarged wide angle picture has an improved depth offield but suffers from reduced image resolution (number of pixels) atthe same time, as compared to the corresponding picture registered withlonger (tele) focal length, thus most likely (again) not entirelysatisfactory as resultant image but nevertheless useful as a templateimage.

These two latter techniques are thus examples of how to produce templateimages according to the depth of field improvement technique outlined inpatent PCT/SE10/02889, where extraction of (spatially) high frequencyimage signals are not used as technique.

A new sensor with several parallel registration-levels arranged indepth, i.e. arranged so that at least two differently-focused images canbe detected, is also suggested in the same patent and this procedureeliminates the need for vibrating sensors (cf above) as well asbeamsplitters (cf below). An image-sensor sharing certain of thesecharacteristics (however for a different purpose), is described by thecompany Foveon (http://222.foveon.com/X3_tech.html; Feb. 17, 2002), asapplied to a camera SD9 from the company Sigma(http://www.photo.net/sigma/sd9). The purpose was here to separate thedetection of three main colours RGB into three separate image planes ontop of each other. These sensor-planes thus being apart but so tightlystacked that their focuses are practically the same.

PURPOSE OF THE INVENTION

Certain conditions and requirements apply to a camera featuring theabove-mentioned depth of field-improvement technique. First of all, aviewfinder mounted sideways apart from the objective lens willexperience a variable parallax, being large for nearby objects and noneat all for objects very far away. Such a finder is therefore notsuitable—at least not at close distance. We are therefore confined tobringing viewfinder-images through the camera objective lens.

Secondly, there are partly contradictory requirements applying to aviewfinder image. On one hand, there is some need for a finder image toexhibit reasonable affinity (though possibly of reduced quality) to theresultant merged picture. But on the other hand, there is also a needfor focusing each individual picture, being recorded at various rangesettings. It's a purpose of the present invention to solve theseproblems. A complete separation of the viewfinder from the imageregistration function is also hard to achieve, considering the fact thatthe objective is the common source for both. It's thus a further purposeto accomplish a digital camera with viewfinder function as well asfacilities for exposure and setting of focal range.

SUMMARY OF THE INVENTION

This invention is comprising the function of such a camera-viewfinder,or to be more precise, arrangements and procedures aiming at improvementof focusing, picture composition and focal range distribution for aso-called depth of field-enhancing camera. The invention is thusapplicable for electronic cameras, generally registering severaldifferently-focused pictures of the scene being projected. Electronicimage-processing may provide means for selecting such image portions orsegments from these differently-focused pictures, being in the mostoptimal states of focus, thereafter assembling these parts for aresultant image with better depth of field than either of the originalpictures. A camera must be aimed at the scene to be photographed and aviewfinder is usually called for in order to accomplish this. For sure,a ‘free hand’ aiming procedure may be chosen by a photographer oncertain occasions, but precision and image control is correspondinglyreduced by that. The viewfinder makes it possible for a photographer tomonitor the depicted scene, usually through an eyepiece or watch animage screen directly without magnifier. The viewfinder facilitatescontrol of image composition and focusing. It may be an opticalviewfinder, meaning direct optical projection without electronicregistration, usually through some telescopic constellation consistingof objective lens, ocular and diffuser plate. Or the finder may beelectronic, meaning that the picture is registered electronically by asensor (like CCD, CMOS). Even the electronic viewfinder might includeoptics, like the projecting objective lens and sometimes magnifyingeyepiece and other optical elements. An instrument- or camera viewfindermay well be regarded as an optical device on its own merits (cfabove-mentioned application PCT/SE10/02889). It is however not operatedon its own, rather constitutes a subordinate part of the maininstrument, this being motive for a separate description. A ‘Viewfinder’is, according to the present text, a device being attached to or beingintegrate part of a camera, presenting (for the photographer) the sceneto be registered. This finder is an optical aid when performingpermanent registration of images, i.e. for image-composition andfocusing. Such recording is presently taking place on lasting media likephotographic film, magnetic tape, memory cards, computer hard-disks, CDand DVD disks.

Other cases where projection-optics may be found, but instead the mainpurpose is immediate observation, do (by definition here) not involveviewfinders: Devices like observation telescopes, surveillance monitorsand sights may apply to these contexts. Such screens and telescopes areused, more or less, for passive display of real-time courses of events.Sights, on the other hand, are being used for active aiming of weaponsand other devices against specific objects or ‘targets’. These latterdevices, designed for (near) real-time image representation, shouldfeature imaging of best possible quality (Cf the above-mentioned U.S.Pat. No. 5,307,170 patent), while a viewfinder image, on the other hand,must not necessarily represent such optimal system resolution: It's nota matter of final result in this latter case, just an image of work,which has to be good enough nevertheless, so that image composition and(occasional) focusing may be accomplished flawlessly.

Functional control of a (main) instrument with depth of field-improvingfeatures (as described in patent PCT/SE01/02889 above) brings aboutspecial viewfinder properties. Or to be more specific, it's here to bedemonstrated, that a camera with capacity to produce depth offield-improved pictures from differently-focused original exposures ofone and the same scene, should also benefit from a viewfinder withsimilar depth of field-enhancing properties. The absence of such aviewfinder renders simultaneous observation (without time-consumingrefocusing) of scene-objects with widely varying distances from thecamera, more difficult. It's becoming increasingly impractical toselect, compose and control a scene to be photographed without such afinder and where instead frequent refocusing of the viewfinder must beresorted to. Experiments and optical theory about depth of field confirmthat a traditional viewfinder, according to prior art (cf below), simplycan not depict a depth of field-improved camera picture with all it'sdetails, because the finders depth of field is insufficient.

Survey of Specific Problems Associated with Depth of Field-improvingCameras

EXAMPLE

A nature photographer wants to take a photo of an ant at 4 centimetersdistance, and of an ant-hill 10 meters from the lens: He can't even seethat Ant-hill through the traditional viewfinder, when having focused onthe foreground ant. Or vice versa with the finder focused on the faraway Ant-hill, he can't see the ant or even tell if the ant is stillthere, part of the scene; It might as well have walked out, away fromthe field of view.

Successful operation, at desirably high speed, of a depth offield-improving camera, may thus be dependant upon an associatedviewfinder, improving the depth of field, however not necessarilypresenting pictures of same high image quality as the registered(exposed) pictures. The viewfinder pictures should, on the other hand,be presented in a (near) real-time mode, even for a still camera,rendering feasible, viewfinder-control of fast moving objects within ascene. This depth of field-extending viewfinder for a still camera musttherefore be in continuous operation, even while the camera itselfremains passive, i.e. when no pictures are being registered. There isthus a principal distinction inbetween the electronic viewfinder and theimage registration of a camera, even where a common sensor is beingused. Refocusing modes, as regards depth of field-improvement methods,being disclosed in the PCT-patent, mentioned above, have the sameprincipal relevance for the viewfinder. It should be pointed outhowever, that the application example, as illustrated by FIG. 1 in thesame patent, with at least two image sensors and (almost) simultaneousexposure at differently-focused image planes, physically separated bymeans of a beamsplitter, does not require any fast-moving components,this constituting an advantage for continuously operated electronicfinders. The viewfinder image may be regarded as a transient‘working-image’ rather than the final result, thus hardly calling formaximum performance as regards depth of field.

For example, reduced electronic processing times apply for viewfinderswith less number of pixels registered or where the number of differentlyfocused original exposures participating in the process, are reduced:This might indeed introduce some extra image blur at certain objectdistances, however not to an extent of hindering image compositioncontrol. Simplified image processing, like pixel by pixel averaging ofdifferently focused original exposures is another option, possiblyreducing image contrast and introducing minor edge-disturbances(generally called artifacts) to the picture. This might seemunacceptable for a resultant still photo, however does hardly disturbthe photographer while working and may thus be tolerated. Such areduction of processing-time favours the (near) real-time function-modeof an electronic viewfinder.

Development of electronic viewfinders is presently fast, moving in adirection of resolution-improvements, however an additional opticalfinder is still in great demand among photographers, due to therealistic picture-qualities and high resolution of such a device.Electronic image processing, aiming at depth of field-improvementsseems, by definition, not relevant for such an optical finder, due tothe presence of photons rather than electrons in said unit. Thislimitation is however compensated by another effect which stems from thehuman pupil reaction: An eye, interacting with the optical viewfinder ofa camera, has an aperture of around 7 millimeters at the most but ismostly confined to something like 2 millimeters in good illumination,which sets a limit to the viewfinders relative aperture, even where theoptical viewfinder happens to have larger aperture. This stop down hasan effect of improving depth of field. The human eye has furthermore aneminent and automatic ability to refocus, i.e. accommodate from about 20centimeters reading-distance up to ‘infinity’, which implies anotherdefacto depth of field-improvement. Anyone can convince himself aboutthe validity of this principle by looking through some magnifyingtelescopic viewer, where an effective depth of field of from at least 2meters up to infinity should be observed with 3 times magnification,which might correspond to some viewfinder concurrent with a minor telelens. The optical viewfinder takes the precedence in this aspect ofdepth of field, over the electronic viewfinder, which latter neitherincludes moderating aperture reduction nor accomodation of thephotographers pupil. There is an important reservation however: Theconcept implies that no diffusive glass plate has been located at theimage plane of the viewfinder. The full-aperture objective lens willproject an image on such a focusing (ground-glass) screen. This imageprojection will thereby associate with a minimal depth of field, beingmore suitable for adequate manual setting of focus. Such a diffusivefocusing screen inserted in the ray path will thus reduce the opticalviewfinders depth of field to about the same level as the electronicviewfinders, implying an obstacle for composition of pictures withinherent large depth of field. Composition of depth of field-improvedimages may thus expediently be performed without such a diffusive plate:The ocular depth of field may thereby be extended from a meter up toinfinity, however this does not imply the similar depth of fieldregarding individual pictures being registered, where (on the contrary)a depth of field interval of—say—less than a meter may occur forindividual photos, exposed through a powerful telephoto lens.

EXAMPLE

The press photographer is standing at an airport expecting a bishop todisembark an airplane, followed by a scantily clad scandal beauty. Thenovember dusk is grey however and the picture must be taken with apowerful tele-lens, without flash light, at full aperture F/2.8 and from20 meters distance. The interval of useful image resolution is estimatedfrom 18 up to 22 meters. The picture value is associated with theimmortalizing of these two celebrities on the same picture, but the‘natural’ depth of field does not suffice because the ‘beauty’ isestimated to emerge up to 5 meters behind the bishop. However, thephotographer being prepared for this eventuality, has brought his depthof field-improving camera with, and is planning for a sharp image withina distance interval of 20+/−25%, i.e. 15-25 meters, by means of Intervalbracketing (cf below). So he sets the depth of field-selector for theabove-mentioned interval. The optical viewfinder of the camera workscoaxially through the camera lens: He is next adjusting the focus,towards the front of the reception committee (about 20 meters distant),with the (diffusive) focusing screen inserted, thereafter folding awaythe same focusing screen. The photographer may now, in a relaxed mood,continue his image composition, for example by means of zooming, asobservable through the optical finder—and then await the right momentfor taking his pictures.

The above-mentioned depth of field-improvement technique with an opticalviewfinder without focusing screen, may prove adequate for mostpress-photographer missions, but may nevertheless turn out as beingcompletely useless when practising macro photography with very shortproximity distances involved. (as exemplified by the Ant and Ant-hillcase above)

It's then possible to relapse into various strategies of mergingdifferently focused images, as described in patent PCT/SE01/02889 andfurther below in this text.

The most elementary finders are aiming devices without opticalcomponents (exemplified by Victor Hasselblad AB's camera 500C/M with the#40215 device), and secondly optical viewfinders in parallel with thecamera lens, frequently occurring on simple fixed-lens cameras (Aclassic example being the Kodak Instamatic camera). The drawback ofthese two approaches is the parallax inherent at close range. Attemptsto solve this problem by means of adjustable search-frames have beenlaunched (Hasselblad XPAN and Leica CL/M), however of little use whenpractising photography with considerable depth of field, mainly due tothe fact that only one object distance at a time may be compensated for,i.e. the method lacks capacity to correctly represent the depthdimension of a scene. Another shortcoming of the separate opticalfinder, is its incapacity to adequately represent variousmagnifications, i.e. fields of view, when zooming. These drawbacks areparticularly annoying when exercising close range macro photography, afrequently occurring application mode for depth of field-improvingcameras. However the exit pupils of independent optical viewfinders areusually small, focusing screen lacking, and this amounts to depth offield improvements. Even such viewfinders do therefore qualify as depthof field-improvers. The simplest viewfinders of that kind, withoutintermediate image-plane, thus lacking diffusive focusing screen, is thecompact low-magnifying so called Dutch telescope with positive objectivelens and a negative ocular, without image inversion, nor opticalcomponents for such purposes.

A common way to avoid the above-mentioned parallax problems is toarrange for an optical viewfinder together with, and usually coaxiallywith the camera lens, however locating a part-transparent or foldingmirror behind, separating the viewfinder image from the picture(s) to beregistered by emulsion film or electronic detectors. The parallaxproblem is thereby eliminated and the viewfinder duplicates theregistered view, i.e. shows the various fields of view andmagnifications generated by focal-distance zooming, as long as thebeamsplitter has been located behind the camera lens. This arrangementmakes a simple separation of lens from camera feasible, i.e. lenses maybe exchanged without influencing the viewfinder function: Suchsingle-lens reflex- or system cameras are more complicated than cameraswith the above-mentioned simple viewfinders, thus more expensive,however being more satisfactory, due to the simple fact that aphotographer may now always and with high precision observe thecomposition of the resultant picture.

The second arrangement, using electronic viewfinders, is feasible forstill photo- and video-cameras with electro-optical detection (likeccd-sensors), and where an electronic viewer is creating (near)real-time pictures. ‘Movie-images’ are thus created on a viewfinderscreen, similar to a TV- or video representation, sometimes being an LCD(liquid crystal screen), otherwise a so-called micro-displayer. Mostvideo cameras have such viewfinders, for the obvious reason thatvideo-film is created anyway, making such a viewfinder presentation easyto accomplish.

This is also a common arrangement among still photo cameras, howeverusually with an image resolution exceeding what can be observed throughthe viewfinder and manual focusing is thereby rendered more difficult.This shortcoming is even more accentuated, whenever the electronic imageis shown without magnifying glass, a nowadays common feature amongdigital still photo- as well as video-cameras. It's true that a generalselection of motive is facilitated by such a procedure, but manualfocusing is hampered by the simple reason that the electronic screenmust be viewed from sufficiently far distance, where an eye canaccomodate. It's furthermore an image of relatively low intensity foroutdoor use in sunshine, an illustration being the C-3000 zoom digitalcamera from Olympus Optical Co (Japan) having two viewfinders: Aseparate optical one and an electronic (LCD) without magnifier. TheDCR-VX1000E video camera from Sony has one electronic viewfinder only: Amicro-displayer being viewed through a magnifier. Methods aiming atdepth of field-improvements, based upon availability of more than onedifferently focused image, depicting the same scene and applicable toelectronic or optical viewfinders, are disclosed in a Swedish patentapplication #0004836-3, being brought further in the subsequent,previously mentioned PCT patent WO 02/059692, from which selectedaspects will now be discussed:

The simplest procedure, relevant for a viewfinder image, created byelectronic means, is apparently some pixel-by-pixel averaging of thedifferently focused images involved. However, the Average-image (M)contrast will be reduced due to inclusion of focused as well asout-of-focus image-information: The unfocused image-components areusually settling upon the final image like a haze (noise), which ishardly acceptable for a resultant image, but might nevertheless pass fora view-finder, particularly when considering the associated fast imageprocessing and moderate computing-capacity needed. The average-imagemethod may be further developed, according to another more sophisticatedand resource-consuming mode, where an essential part of theabove-mentioned image haze from un-focused information is extracted fromthe Average-image so that contrast and image quality is bettered. Afurther improvement may be accomplished by means of introducing a simplesegment-selection method, even though certain disturbances along edgesmay emerge, however this being of less consequence for sequences ofchangeable images rather than still photos.

Superposition of differently focused images is even feasible for anoptical viewfinder, again ending up with weakening image contrast due tocontributions from in-focus as well as out-of-focus image information,however still a potentially useful viewfinder application. One mode isto split the wavefront or aperture in at least two parts, then introducedifferent states of focus for these ray paths, by optical means, andfinally perform an optical reunion of the two parts into one image,constituting a superposition of differently focused contributions (FIG.3 b).

Another and now time-related method is to introduce periodic change offocus, so that differently focused pictures alternate fast enough(ca>=10 Hz) in order to create an illusive impression of images beingmerged for an observer, like what's happening when watching video ormovies. These above-mentioned methods, related to optical viewfinders,are here to be regarded as depth of field-improving techniques. The onecamera viewfinder function is thus control of and—whereapplicable—manual setting of focus. This is furthermore repeated severaltimes when operating a depth of field-improving camera with severalfocal planes to be focused upon.

This is a relatively tedious, but in some cases acceptable process, whenphotographing static scenes more or less, and where optimal focusing ofspecific objects has priority. It's here to be named the ‘Manualfocusing mode’.

The depth of field-improvement process may, according to another notion,be regarded as a joint action of several differently focused picturesput together, so that a more or less continuous succession of field ofdepth-intervals are added to each other. There is thus emerging aquestion about how an optimal distribution of these focuses should looklike. This may—following known theory—be calculated with some opticalcomputer program.

EXAMPLE

Let's say the digital camera focal length is f=20 mm with a relativeaperture F/2.8 and where the aim is to have a depth of field-intervalfrom the horizon down to shortest possible proximity. Furthermoreassuming the optimal axial image resolution to be equivalent to aRED(75%)=0.03 mm while the image definition must nowhere exceedRED(75%)=0.07 mm within the chosen interval (RED is the radial energydistribution). The interval of acceptable image resolution will thendepend upon the number of differently-focused exposures of the sequenceinvolved, or (below) the number of sensors, following a beamsplitmethod:

TABLE 1 Number of sensors Depth of field (distance-interval) 1 4.5meters-∞ 2 2.3 meters-∞ 3 1.5 meters-∞ 4 1.1 meters-∞

Another table, showing the range of focus for each of these sensors andthe effective depth of field mastered by each sensor, may similarly becalculated. This constitutes an example of optimal distribution forobject-distances in focus, and a depth of field-improving camera with af=20 mm lens

TABLE 2 Sensor Number # In-focus Object Distance Depth of field interval1   8 meters 4.5 meters-∞ (infinity) 2   3 meters 2.3-4.5 meters 3 1.8meters 1.5-2.3 meters 4 1.3 meters 1.1-1.5 meters

It's thus apparently easy, following established optical theory, tocalculate those object distances answering to the most evenlydistributed image resolution, over a certain interval. However, thisdistribution is determined by circumstances under which thedifferently-focused images were exposed, or specifically the total(object) distance interval (like from 20 cm up to infinity), the numberof frames (like 3) being exposed within this interval, the focaldistance/magnification chosen (like a f=60 mm telephoto lens for digitalcamera) and finally the relative aperture in use (like F/2.8); Fewexposures, long focal lengths and large apertures are reducing theuseful depth of field. The photographer may therefore have some goodreason to decide about the depth of field-interval within which he isinterested to operate. This may be done by using an Interval-Selector.Or to be more specific: There may be good reasons to avoid focusing atdistances closer than those objects he intends to compose into thepicture, because the sensors have to be located near each other there(cf table #2 above) and the selective image processing is rejecting suchsegments nevertheless. It may therefore frequently turn out practicalfor the photographer (while performing his initial picture composition)to focus upon the nearest object of the scene and ‘lock’ the proximitydistance there, using a Proximity-Distance Selector. This may involve anautofocus procedure, however some photographers may still persist inusing manual focusing in order to secure better control. Axial movementsof an image-projecting lens, individual parts of it, or the imagesensor, may effectuate sequential refocusing or it may be done with someoptical element introduction, like inserting glass-plates in the raypath, thus altering the optical length, causing the image-planes toswitch. Using more than one (differently-focused) detector, a mirrorelement may be moved in or out of the ray path so that imageregistration can alternate from one sensor to another, or apart-transparent/reflecting mirror element may allow simultaneousregistration of several pictures to take place. These methods can becombined.

The need to monitor, control and perform the above-mentioned close-rangefocusing and furthermore to scrutinize the depth of field at close rangeand further away, is creating a need for individual evaluation of theproximity picture to be registered. The above mentionedviewfinder-capacity to improve depth of field must therefore be switchedoff, when need arises, replacing the finders processed and merged viewwith individually focused primary-images instead.

The implementation of this might involve some push-button procedurewhere a finder-view of preference, like one of the four individuallyfocused images of table 1-2 (above), may be chosen by means of‘clicking’, however with an optional return at any moment to theabove-mentioned composite image, with extended depth of field.

This mode of locking on the closest range will here be called‘Proximity-Bracketing’, including a subsequent and automatic setting ofimage-focuses, in order to achieve an optimal distribution, followingthe principles outlined for the Tables (above). This automaticrefocusing may consist of axial movements of individual image sensors,where motion-generating motors, piezoelectric actuators etc areeffectuating the movements, being under control of an electronic devicewhich calculates, or stores in memory (or both) all possible sets ofoptimal focusing distributions for the system. This Proximity-Bracketingmode may thus be classified as semi-automatic, involving one focusingoperation only, namely towards a nearby object, after which the rest ofthe focusing is done automatically. It may, according to another notion,be regarded as a depth of field high-pass filter. An analogous low-passfilter would of course be feasible as well.

Another semi-automatic mode, already mentioned (in connection with the‘bishop and the scandal beauty’ above) is the ‘Interval Bracketing’method involving choice of and focusing on a priority-object (Sensor orimage detection P), using an (optimal-) Focus-Selector and furthermoresetting a (depth of field-) Interval-Selector for an object distanceinterval (around the same object), within which an acceptable depth offield is required: The shorter interval limit may for example correspondto a distance/sensor P− while the farther limit corresponds to anotherP+. Thus a photo with acceptable image resolution will emerge inside theobject-distance intervalP−<P<P+  (1)

And this constitutes a depth of field Band-pass filter according to analternative notion.

A purpose with this method is thus to solve the prevalentpress-photography problem of today, where the aim is to simultaneouslyfocus upon two laterally (i.e. sidewise) nearby, however in depth moreseparated objects, like portraying two persons. The trick of compressingsuch a scene in depth, by using a strong telephoto lens, is commonlyshared standard art among photographers. However, a reduction of depthof field is the side-effect, leaving only the priority-object in sharpfocus while other in depth-deviating objects remain blurred more or less(as being evidenced almost every day by the daily press). IntervalBracketing shows close affinity to the present day procedure, whichpress-photographers are used to: Setting a Manual- or Auto focus againstan object of priority, through the finder, and then make the shot asusual, the only difference being a preselection of desired depth offield, like +/−5 meters which corresponds to +/−25% at 20 meters range.

Even this is a semi-automatic method, with manual selection ofpriority-focus and depth of field interval, while other focal conditionsare set automatically by means of an electronic control, essentiallydescribed already under the title ‘Proximity Bracketing’ above.

Another procedure involves some continuous ‘automatic’ priority-focusingby means of an Autofocus-procedure (prior art), usually aiming with thecamera finder against the object chosen, however otherwise sametechnique as already outlined.

Regions outside the bracket-interval may also be set even more out offocus, following a conceptionally similar but, as to the effect,dramatically deviating method. The image definition will thusdeteriorate even further outside this interval (1) above. The effect isachieved by means of a negative segment-selection process, beingdescribed elsewhere as a depth of field-reduction method (patentPCT/SE01/02889); Image information outside the depth of field bracketinterval is thereby suppressed, making visual for- or backgrounddisturbances less obtrusive. ‘Special effects’ may also be created.Objects in focus within the selected interval will on the other handexhibit increasing contrasts from its high resolution against a blurredsurrounding: It's an advantageous method for electronic finders, wherethis effect may enhance objects to be focused upon and may also aid aphotographer in concentrating his attention to vital image-parts ofpriority, during image composition. Another procedure: The mostprevalent or (according to some other criterion) otherwise preferredfocal states within a scene, are automatically identified and selected,the image registration thereafter taking place, observing the samestates of priority. This latter may be the result of an Autofocus scan,where best focus is measured at certain positions over the field ofview, which may also be divided into segments according to a furtherdevelopment of this mode, where the same measurement is now taking placein each individual segment.

And finally, there are fully automatic methods, aiming at a morestereotyped distribution of focuses according to some standardprocedure, as optimal as possible within a given interval. This is avariety of the Proximity-Bracketing mode (above), however differing inthat the closest distance is preselected. The advantage of this mode isspeed because no ‘thinking’ is necessary. The reaction time is fastestpossible because no camera settings whatsoever are called for, not eventhe reaction time for an Autofocus (normally about ½ second) isdetaining the exposure. There is an objection that this method is rarelyoptimal for a specific scene. On the other hand, the common problem of afailing Autofocus, where the lens is focused at the wrong distance, forinstance because of an aiming error with the finder, is now avoided.This method is therefore particularly suitable for amateur photographersof the general public, where simplicity and reliability are at premium.Our name for it is the ‘Standard focusing method’, not to be mixed upwith some Autofocus mode, which in a sense is the very opposite of it.Several of the above-mentioned beamsplitter examples call for 3 or even4 image sensors. A simple estimate tells that each sensor will thenreceive only ⅓ or ¼ of the incident light at the most, the latteranswering to two steps of Aperture reduction, which may be todisadvantage in a gloomy environment. The alternative is sequentialexposure while refocusing and with one sensor only, which is certainlygiving full illumination from the lens all the time, however must bedone fast enough in order to avoid motion blur. Not leastpress-photography of fast-moving courses of events may suffer from this.There are instances however where a photographer is satisfied with (forexample) two distinct focuses only, like when portraying two personsagainst a heavenly background and where no significant details appear atintermediate distances. A need for optimal focusing of these twopriority objects will then emerge. Only two image sensors are requiredin this case, other sensors might as well be inactive. Advantages withthis arrangement include fast image processing and fewerexposures/sensors needed. The above-mentioned problem with lightreduction may persist however. This situation may be improved upon bylinking up the reading of sensors as follows (example):

Assume there are 4 image sensors available while (cf above) only twodifferently focused images are required. The sensors may then work ascouples, i.e. the electronic registration from two sensors, focused foridentical object distance, are connected. The two other sensors beingdifferently focused are similarly coupled. The luminous flux generatingan image of a certain state of focus is thereby doubled which—true—isnot the same as to double the sensor sensitivity, yet the improvementwill be significant and this pixel-by-pixel addition of images will alsodecrease the spatial noise, being different for the two sensors, andpicture quality will increase correspondingly.

Referring to the mode of Interval Bracketing (cf above) and another4-sensor design, it would be possible to join two sensors forregistering the priority (middle) state of focus (P) and thereafterregister the interval ends (P− and P+) with one sensor each. This willgive us a better registration of priority focus, thanks to the doublingof the sensors, however the relative intensity from the three picturesmust be electronically adjusted in order to obtain same averageintensity.

No doubt, there remains a multitude of other practical ways to elaboratethese focusing- and sensor-strategies but a further variative account ofthe same topic would hardly add much of new principles to this text. Theexamples given are illustrating the principles of the present invention,but do not confine the scope to that. ‘Camera’ and ‘Digital Camera’ with“Viewfinder” are denominations common in this text as regards theinvention, but it should be emphasized that the invention is equallyapplicable to video-, surveillance-, lowlightlevel-, and TV-cameras plusImage-intensifier- and Infra-red cameras, just to mention a few otherexamples of instruments which may be focused, which may have finders andwhich are meant for permanent image registration, being suitable for adepth of field-improving technique.

FIGURE DESCRIPTIONS IN BRIEF

FIG. 1 shows a depth of field-improving camera design, including theviewfinder.

FIG. 2 shows another such camera.

FIG. 3A-D exhibits further examples of beamsplitter arrangements for acamera with finder and with depth of field-enhancement capability.

FIG. 4A-C shows another advantageous design with a beamsplitter ofdynamic character at the moment of exposure.

FIG. 5 depicts a common digital still camera, being modified in order toproduce depth of field-improved photos.

DESIGNS EXEMPLIFIED

FIG. 1 exemplifies a depth of field-improving camera with optical andelectronic viewfinders, all having the capacity of extending depth offield, according to the invention: Simultaneous registration of up to 4differently focused images is possible according to this set-up, usingthe four sensors D1, D2, D3 and D4. The split into different pictures iseffectuated by means of the right-angled beamsplitter prisms RP, P1 andP2, where the mirroring surfaces are PS1, PS2 and PS3. These prisms areby preference made of light-weight glass with high refractive index, inorder to shorten the optical path through them. Such beamsplitting mightbe arranged by using many other kinds of prism- and mirrorconfigurations (like involving some kind of Pechan prism), some of themwith even shorter optical ray paths. However we have here gone for thissimple and illustrative example which is furthermore offering identicalray paths for the four images, as far as optical correction isconcerned. Better-quality cameras with beam splitters and severalsensors are available on the market (like the so-called 3 ccd videocameras), however the purpose is differing there. A camera lens [OBJ]will rarely perform with its sharpest image resolution at close rangeand there is furthermore a practical limit as regards sensor movements:The sensors are here focused by means of axial movements, thus beingfocused near infinity when close to the prisms as shown in FIG. 1. Axialmovements prompted by such variable object distances and associated witha camera lens [OBJ] of focal length f=50 mm is further indicated by thefollowing

TABLE #3 Object distance Associated axial focused at movement of asensor Infinity ∞  0 mm (millimeter)  1 meter  1 mm 20 centimeters  5 mm 8 centimeters 15 mm

The sensors are moving away from the prisms in FIG. 1 when refocusingfor proximity distance. In an effort to optimize the use of projectedlight through the objective lens, we have here chosen a system whereeither sensors or the optical finder is getting all the light: This isbeing effectuated by means of a movable mirror S3 (here shaped as aprism half), which is inserted into the ray path behind objective OBJ,when using the optical finder. Mirror S3 is here attached to the top ofa movable beamsplitter prism RP and these two components RP and S3 arethus moving vertically together when changing inbetween the two modes ofeither optical finder or electronic finder & image registration. Thebeam is deviated vertically upwards to an image plane with a diffusivefocal plate M inserted, and with the prism-assembly RP/S3 loweredaccording to the figure.

This is consequently a finder-image being projected, corresponding tothe detector-image planes, and furthermore magnified by means of a‘transport-lens’ MOB, projecting onto an eyepiece image plane OB viamirror S1, creating an image of about same size as on the liquid crystalscreen LCDB. The photographer may observe this image OB from the exitpupil position PU1, through the low-magnifying ocular OK, and the mirrorS2 must then be folded to its upper position. He may instead observe thecorresponding electronic picture LCDB when lowering mirror S2. The issueof using a common eyepiece for optical and electronic viewfinders hascome up quite recently, i.e. whenever two such finders may occurtogether in a digital camera. The arrangement allows for ocularobservation of the photographic scene, through both finders and withoutchanging observation/pupil-position, this amounting to a practicalfeature. Only one eyepiece is furthermore required for magnifying twodifferent pictures, which may be attractive from a cost- or design pointof view, reducing size and weight. This arrangement with a commonfinder-eyepiece may advantageously be applied to many other kinds ofelectronic, so called digital cameras, with one optical and oneelectronic finder, where the aim is to magnify both images with alens/ocular. (FIGS. 2 and 3 are illustrating this further). Mirror S2 isin fact folded into a removable lid (including the mirror) and thisremoval makes it feasible to watch the LCD image screen from above,constituting a classic mode, sometimes preferred by photographers. Thepicture LCDB will appear upside down when looking from above, however oflittle consequence here as the image may readily be turned the right wayround again by electronic means. One mode of preference is to turn thisimage automatically when detaching the lid & mirror. Even the focusingscreen M in the optical finder's ray path may be folded aside, giving adepth of field-extension to the optical finder, in fact functioning as aterrestrial telescope, as already described in this text. The mobileprism RP is displaced to a more central position inbetween the otherbeamsplitter prisms P1/P2 and objective OBJ, when switching from opticalto electronic finder-view or image registration. Mirror S2 is at thesame time automatically folded down, according to an attractive design,making the electronic image-screen visible through eyepiece OK. Thewhole ‘other’ beamsplit-assembly P1/P2 including its mobile sensors, isthus stationary and mechanically linked together, constituting a stableopto-mechanical unit. The images associated with D1 and D4 are invertedvs the corresponding pictures D2 and D3, however this is corrected byelectronic means. The optical mirror-prism S3 answers to the flippingmirror of a single-lens reflex camera, which means that it's swiftlyfolded away while the photo is taken. We are instead having a verticalmovement here of prism RP, however the vertical mechanical tolerancesare not so critical since the subsequent beamsplit takes placehorizontally. The camera is capable of performing electronic processing(not shown in the figure) of the differently-focused images, in order topresent a depth of field-improved view via the electronic finder LCDB. Alens L2 for possible optical correction ofbeamsplitter/prism-aberrations is also suggested and other suchcorrective elements may be added as well (not shown).

The figure is also indicating a teleconverter TK, which may be attachedat the front of the main lens OBJ. This is, according to a preferreddesign, an afocal zoom, making it possible to change the focal length. Astationary standard objective lens may protect the interior of a cameraagainst moisture and dust, this being less important for the classiccamera, where emulsion-film exchange is taking place all the timeregardlessly, but more important for a digital camera, which isconsiderably more sensitive in this respect. A design following FIG. 1having a fixed rather than exchangeable lens plus an afocal detachablezoom, is thus defacto preserving the feature of focal-length zoomingwhile offering better protection as well. The lens OBJ must however giveenough available free space inbetween rear lens surface at L1 and theimage plane, this distance usually amounting to 40 millimeters or morefor generally available single-lens reflex (24×36 mm) camera lenses.FIG. 1 is more of a principal character, though reasonable proportionswere yet aimed at.

Even FIG. 2 is presenting an example of a video and/or still camera forimproving depth of field, however with one image-sensor only, stillfeaturing optical as well as electronic finders, both with depth offield-improvement capacity. Refocus of sensor D is, according to thefigure, effectuated by means of a rotating plate RP, which may hereconsist of—say—three parts: Two plane and parallel glass-plate segmentsof different thickness plus one sector without glass: The camera maythus be refocused inbetween these three focal states when rotating theplate around its axis A. Axial and cyclic movements (vibration) of thedetector D or some other internal process inside lens OBJ might also dothe trick, referring again to the Swedish patent application 0004836-3,where all these techniques have been outlined, thus not to be dwelt onany more here. Such periodic refocusing will thus generatedifferently-focused images, which may form a basis for improving thedepth of field for images being registered, as already described, plusat the same time generating, using same process and sensor, acorresponding depth of field-improved view at the micro-displayer MD,which can be observed from exit-pupil position PU, via thedisplay-mirror-prism DP, magnified by the intermediate objective lensMOB and the ocular OK. The oblique-angle view from above may provepractical in cases where the photographer wishes to descend his camera,down to ground level, from where a depth of field-improvedmacro-perspective may look ‘interesting’. The prism element DP may bereplaced by a thin mirror, however whatever the actual arrangements maybe, the mirror-element DP can be folded outside or be slided away fromthe beam (this latter in right-angle direction from the figure-plane).The camera suggested by FIG. 2 has a small sensor (about 6×8 mm), thuspreferably working with ‘video-size’ lenses, where typical focal lengthsare f=8 mm, f=16 mm or f=50 mm (long telephoto lens). These lenses haveusually a relatively short free space inbetween rear lens surface andimage, being a possible obstacle when attempting to insert abeamsplitter behind the lens. The beamsplitter SP chosen here, for theoptical finder, has therefore an unusually short optical length (intransmission), due to an arrangement with 30-degree angles and a doubleinternal reflection. The prism becomes even more useful by usinglow-weight high-index glass. This prism is thus reflecting away some ofthe light projected by lens OBJ, into the optical finder, where anintermediate image B of same size as at Sensor D is firstly created,thereafter being magnified to another ocular-image-plane, where afocusing screen M has been inserted in order to facilitate focusingthrough the optical finder, as already explained (above). The focusingscreen can be folded or slided away, when using the optical finder inthe depth of field mode (described above) or when observing theelectronic finder-view at MD. The optical finder without focusing screendoes then function as a so-called terrestrial telescope and it should bepointed out that this arrangement allows for more comfort than if theprimary image plane is watched directly through an eyepiece (cf FIG. 3),because such an eyepiece must hare a shorter focal distance due to thesmall image size and thus a shorter eye relief, being an inconveniencewhen viewing. The image here, may be magnified instead, thanks to theoptical ‘transport system’ MOB, making it possible to use a larger sizeocular. The projected light is thus split inbetween optical viewer anddetector D, by the beamsplit-film S of the stationary beamsplitter prismSP, this constituting an attractive procedure, because movablecomponents are avoided. It's true that, as a consequence of this, thecamera sensitivity will decrease while the finder view becomes slightlydarker, however this trade-off may still be acceptable, because thecamera has only one sensor D, so the light must not be further dividedinbetween several detectors. The example of FIG. 2 is only meant toserve as a sketchy guidance as regards the principles involved, yetreasonable proportions were aimed at.

FIG. 3 is again exemplifying a camera with depth of field capability,this time a compact and sketch-oriented design, having bearing upon acompact video camera with still photo capacity, with two differentlyfocused sensors D1 and D2 plus an optical viewfinder, where the eyepieceOK is this time focused upon one of the primary image planes (generatedby beamsplitter-cube P) of the camera lens OBJ. The optical finder isthus coaxial with lens OBJ, having relatively small pupils and lackingfocusing screen, thus offering considerable depth of field. The image ofthe electronic finder is generated by image-sensors D1 and D2,presenting a finder view at micro-displayer MD, which becomes visiblethrough the eyepiece OK, as soon as the finder-prism SP is slided aside(vertically in FIG. 3), i.e. away from the beam. Electronic—as well asoptical finder-views are hence created in the common primary ocular (OK)image plane. The photographer may now choose (by using an image-selectorfunction) inbetween electronic finder-views from either detector D1 orD2 (for focusing), or a processed image aiming at extended depth offield, merged from D1 and D2 (for image composition). FIG. 3 a shows theprimary beamsplitter cube in some detail: It has three half-transparentmirrors R1, R2 and R3. The detectors D1, D2 and the optical viewer willthus get 25% each from the incident light while remaining 25% is lostdue to reflection back through the lens again. The light at detector D1has been transmitted through both mirrors R1 and R2, the light atdetector D2 was reflected by mirror R1 and then transmitted by mirrorR3. The light to the optical finder thus passing two opticallyequivalent ways as follows:

-   a/ R1(T)-R2(R)-R1(R) and out through free exit A (no mirror)-   b/ R1(R)-R3(R)-R1(T) and out again through the free exit A    where R is reflection and T is transmission

Each of these contributions are thus 0,5×0,5×0,5=0,125 of total lightintensity thus in total 2×0.125=0.25, being 25% of incident light. Thesetwo ‘contributions’ must of course be lined up carefully in order toavoid double-imaging, however probably not a big deal in this casebecause of solid physical integration of the beamsplitter-structure andfurthermore short optical lengths.

An introduction of asymmetry (PA) in the beamsplitter ray-path (FIG. 3b) may introduce a (relative) focus-difference inbetween these twobeam-parts of the optical finder, being an example of how twodifferently-focused images may be generated optically with awavefront-split, subsequently being superposed again, the aim being tocreate a kind of optical average-image, thus improving the depth offield. It would be possible to slide out the prism P, replacing it withanother beamsplitter PS, introducing at least one more image plane D3,for sequential registration of additional and differently-focused images(located in another figure-plane, just hinted at.).

FIG. 4 a shows a beamsplitter arrangement in perspective, with twovertically movable mirrors S1 and S2 and the three image detectingsensors D1, D2 and D3. The two mirrors are usually reflecting as well astransmitting and are, according to a design of preference, attached ontop of each other in right angle. Incident light from the scene, whichis to be photographed, is passing an objective lens with exit E,thereafter being transmitted by either mirror S1 or S2 and finallyprojected against the in-focus image plane of sensor D1, beingcontinuously illuminated. Another part of the incident light beam iseither deviated in right angle by mirror S1 against detector D3 to theright or by mirror S2 against the detector D2 to the left in the figure.A switch inbetween image detection at detector D2 respectively D3 may beeffectuated by vertical movement of mirrors S1/S2. Axial movements ofthe three sensors D1, D2 and D3 may focus them differently and twodifferently-focused images may always be registered, either D1 and D3 orD1 and D2. According to a preferential video camera set-up, one of thesesensors (like D1) will vibrate in an optional but for video purposesadapted frequency, this generating cyclic refocusing. Piezoelectricactuators exemplify the means to accomplish this, having the capabilityof vibrating several-gram-weight objects at frequencies exceeding 25 Hzand with amplitudes more than a millimeter, answering to an actualfrequency of refocus. Anyone of these three detectors of FIG. 4 a may beexchanged with the path of an optical finder. FIG. 4 b shows the samebeamsplitter system from above and FIG. 4 c from the side. The threepart-FIGS. 4 a, b and c are thus exemplifying a beamsplitter system,essentially made up from two movable mirrors, accomplishing simultaneousregistration of two differently focused images plus at least twosequential but differently focused images or several more of these, incase one of the image sensors is set into periodic vibration forth andback, as may be considered in a video recording application. Detector D1may be eliminated if the mirrors are totally reflective, leaving the twodetectors D2 and D3 for alternating and time-sequential imageregistration.

Another application example (FIG. 5) features sequentialimage-registration, using a commonly available digital still camera(CAM) adhering to prevalent techniques, with the normally associatedfunctions like electronic viewfinder (LCD) with magnifying lens (LUP),objective with lens-components (L), image sensor (BS), image memory (CM)with an exit (EXP) for exporting pictures to a PC computer (where thedepth of field-enhanced pictures are being processed). And furthermorean exposure-control, making photography in the so called C-modefeasible, implying rapid registration of an image-sequence, whilekeeping the exposure-knob (CK) depressed. High picture-frequency isaimed at: Current simple digital cameras can make about one shot asecond in C-mode (Like Olympus Camedia C-3000) while more professionalcameras (Like Canon D30) may produce 3 sequential pictures per second,or even more. The focus is controlled by means of a motion actuator, inthis case a Focus-motor (FM) which, according to this example, is movinga Focus-lens (FL) forth and back along the optical axis of the cameraobjective (OBJ). A design of precedence, which is defacto transformingthis standard-camera (prior art) into a depth of field-improving camera,is involving an electronic module EM for driving the focus-motor FM, thepurpose of this being to refocus the lens according to the intentions ofthe photographer while a continuous mode of exposure is on. Thisconcerns an automatic, programmed procedure, where the focus is usuallyset to preselected states during the intervals inbetween exposures. Anexample of such a course, involving 3 states of focus (‘images’) incontinuous mode and about one picture/second goes as follows:

TABLE 4 Time lapse Event 0 second First frame exposed at startingposition #1 0-1 Refocus to focal position #2 - then standstill there 1Exposure of the second frame 1-2 Refocus to focal position #3 - thenstandstill 2 Exposure of the third frame 2- Refocus to Starting position#1 again

Continuous Autofocus-mode photography is a common feature nowadays,however does not allow for controlled preselection of focusingranges—therefore being of little relevance to our application. It may(typically) take 0,2 second to refocus, making the rest-time for eachstate of focus about 1−0,2=0,8 second in this case. Exposure times aretypically shorter—like 1/125 sec in this example. Firstly, this gives‘plenty of time’ for the camera to expose inbetween refocusings, andsecondly, the individual pictures will not suffer from moremovement-blur than at ‘normal’ photography with single shots. However anobject in view might still move considerably inbetween two shots: Minorfast-moving objects with unambiguous states of focus, belonging to justone of these differently-focused original exposures will often show upwithout appreciable blur or other disturbances, after segment-relatedimage processing. Discrimination or enhancement of mobile objects, aftersome motion-vector analysis, constitutes a furtherimprovement-potential. However the present example of a depth offield-improving camera is best fit for photography of semi-stationaryscenes like still lifes and landscapes. An increase of frame-frequencyto about 3 or 10 exposures per second should make it increasinglypossible to master more mobile scenes, like people sitting at a pressconference. Pictures are thus taken of the same motive but differentlyfocused, constituting a necessary basis for electronic image processingand production of depth of field-improved pictures as already described:However the image processing is not taking place inside the standardcamera according to this example (FIG. 5) but by using program-softwarein a separate PC computer, located somewhere else. The photographer mayalways relapse into a defacto ‘traditional’ one-exposure mode, usingindividual original exposures in incurring cases of abortive depth offield-processing. The state of focus, i.e. position of the focusing-lens(FL) is controlled by at least one position-sensor (LS) and/or by meansof so called ‘dead reckoning’ within the operative object-range intervalchosen, involving registration and feed-back to the electronic module(EM) about movements of the same lens. (FM) may for example be astep-motor, run on pulses from an electronic driver-circuit (D) whilethe movement-registrator is composed of an electronic counter (R),counting the plus/minus number of ‘steps’, which the motor is drivingthe focusing with, in a direction against or away from a calibratedfocus-position, being determined by a Position-sensor (LS). TheSystem-processor (P) is aided by this kind of information whenconverging the focus into a requested position or state. This and manyother alternative arrangements involving other motions-sensors (Like forUSM-motors, Piezoelectric actuators etc) and other positional sensors(like mechanical, optical and electronic terminus-, rotation- orcalibration-sensors) belong to prior art. An analogous displacement ofthe image sensor(s) (BS) or other lenses in objective OBJ may also dothe trick, instead of moving the rear lens (FL). The module EM, being incontrol of this continuous-mode refocusing is, according to FIG. 5,located outside the existing standard camera-body, emphasizing adistinction inbetween this depth of field-extending camera and astandard digital camera. However, this module EM might as well beintegrated inside the digital camera. The standard (CAM) digital camera(Like Olympus Camedia C-3000) and electronic module EM are, according toFIG. 5, defining a depth of field-improving camera, with sequentialrefocusing. The lens OBJ may be detachable and furthermore supplied witha focusing motor and electronics of it's own (like for objectivescompatible to the Canon D30 camera), thus making it analogously possibleto drive this lens by an electronic module EM. However such a separateand detachable lens can only register images when interacting with acamera-housing and may thus nevertheless and under these circumstances,be regarded as an operational part of a camera, thus by definitionincluded in the application-example described.

A prerequisite of this automated focusing procedure, synchronized withan ongoing continuous exposure-mode, is that the focal states wereselected in advance. It has already been described how an operator maychoose inbetween various preselection-modes like Manual focusing,Proximity-bracketing, interval-bracketing and Standard focusing,involving various levels of automation, A fast manual focusing-mode withadvantageous user-ergonomics may be used in the example of FIG. 5, asfollows: The depth of field-improving camera has a two-step shutterrelease knob (K) with at least the following three functions:

-   -   Focus-registration    -   Picture-number selection    -   Exposure

Two-step knob (K) means that it can be pressed down to two different,distinct activation-levels. This is normal for cameras (prior art),where the camera electronics is activated when pressing (K) half-way(The normal intermittent Autofocus mode becoming activated) and exposurefor a picture takes place when pressing the same knob down to thebottom. The distinctive feature of the depth of field-extending cameraof FIG. 5 is that registration and saving of current state of focus,into an electronic memory (FM), is taking place at the moment when theknob is depressed half-way. Registerable information about this state offocus, originating from position-sensor(s), counters etc have alreadybeen outlined (above). Other focal states can be saved by repeating thisprocedure, i.e. priority-selection of sets of focuses may continue untilall memory capacity of the system has been fully utilized. Afocus-indicator, like the light-emitting diode (LD), is lit whenever astate of focus is activated: The number of diodes being lit, will thusdisclose the number of pictures in a focusing-sequence. This sequentialpreselection and memorization of focal states is usually preceded bymanual- (MF) or Auto (AF)-focusing against objects within the scene tobe photographed, i.e. objects being alloted priority by thephotographer, and being predestined for optimal image definition. Thephotographer has the option to either set manually for best imageresolution, as appearing in the viewfinder, or set for specific numericranges on a designated range-scale, designed for this purpose. Anoperator changing his mind, may press the Reset-knob (NUL) whichrestores/nullifies the focus-memory (FM). Light-diodes (LD) are thenturned off and it's then possible to start from scratch again with thefocusing. This reset may also be effectuated by twisting a universalknob (K). A number of such memorized focuses, meant for acontinuous-mode sequence, constitutes by definition a ‘set’ of focalstates. Such sets may be memorized in a specially designated memory (SM)for later requisite and be brought up again (by a Focus-retrievalcontrivance) by using additional knob(s) SK. Such a procedure may provepractical when repeating the photography of a specific scene—without theunnecessary repetition of time-wasting refocusing. The photographer,having depressed the knob K half-way (thus saving a focus), has eachtime the option to either release the knob or complete the pressing,this latter triggering off exposure of the number of shots answering tothe focuses being saved in memory (FM). The electronic module EM willthen drive the Focus motor (following the principles outlined above), toeach memorized state of focus, where image registration is subsequentlytaking place. This process is controlled by a computer-programassociated with the microprocessor (P), which determines order ofpriority, refocus-speed, time of standstill at respective focus etc. Theknob (K) is thus functioning as a Focus-registrar when (1) pressing downhalf-way, then as a picture-number selector and exposure-trigger at themoment (2) of pressing down completely. The entire course of events fromfocus-selection until finished exposures thus being controlled with oneknob only and without change of grip, supposedly making a camera easierto handle. However, any specialist may readily appreciate the fact thatthe configuration/layout of knobs, signal-lamps etc may varyindefinitely. Light-emitting diodes may be replaced with numeric symbolson a LCD-display while the universal-knob (K) may be replaced withseparate knobs or other controls, using one for each individual functionand in variating combinations. It would for instance be feasible tocontrol each single focus-memory with an individual knob: We are heretalking about minor variations around a main theme.

The existence of adequate procedures for memorizing states of focus anda device for automatic refocus of a camera, while sequential imageregistration takes place, are essentialities however.

FIG. 5 is schematic and simplified, i.e. shows only certain detailswhich are relevant for the discussion above, neither pretending to be inscale nor showing the complete electronic set-up.

1. A digital camera with lens for depicting a scene being composed ofobjects within a field of view, at various object-distances in front ofsaid objective, a focus-selector and a focusing device for setting thefocus of the camera at different distances, at least one electronicimage detector with entrance plane for detection and register of imageinformation answering to an image of the scene being depicted, plus anassociated image-sharpness detector, wherein a) said focusing devicebeing arranged for simultaneous focusing of this instrument at differentobject-distances, and/or a time-sequential focusing procedure is beingused, b) an image detection being arranged in such a way that imageinformation equivalent to at least two differently-focused images, i.e.with mutually different states of focus and depicting the same scene,are detected, c) means being allocated for letting said image-sharpnessdetector, directly or indirectly and from each such set of correspondingdifferently-focused images, select/extract and forward suchcomponents/parts of the image information, which contribute to the mostoptimal picture definition and let this said selected image informationfrom the same set of mutually corresponding pictures, merge into a finalimage with better resolution than the differently-focused imagesdetected individually, and d) means being arranged for selectingindividual focus-distances, using said focus-selector, answering to atleast one of said differently-focused images, this constituting anoptional pre-selection of individual states of focus, before imageregistration takes place; wherein the camera is furnished with afocus-registrar contrivance and at least one focus-memory, wherein meansare arranged for registration of single states of focus as well as setsof such priority-states and furthermore forward such information to saidmemory for saving.
 2. The camera of claim 1, in continuous mode, i.e.with capacity to perform a swift time-sequential succession of exposuresand further means being allotted to control and drive said focusingdevice by using an electronic driver-module, wherein means are arrangedfor automatic setting of the camera focus at said pre-selected states offocus, while image detection, i.e. said exposures, are going on.
 3. Thecamera of claim 1, and with additional motion-sensor, calibrated counterand electronic processor, wherein means are arranged for saiddriver-module to electrically drive the transport of such opticalelements or image-sensors, being primarily responsible for refocus andthat said calibrated counter is arranged for registration of currentlocation of said focusing elements and that this information isinteracting with the processor in a procedure of converging said motiontowards a required state of focus.
 4. The camera of claim 1, furnishedwith a focus-retrieval contrivance, wherein means are provided forselecting and retrieving information from said focus-memory, thisinformation constituting registered sets about focal states or partsthereof, i.e. in-data for controlling said focusing device.
 5. Thecamera of claim 1, and provided with a focus-indicator, wherein meansare pre-arranged for visual indication of state of focus, beingregistered in said memory.
 6. The camera of claim 1, with a nullifiercontrivance, wherein means are adopted for an electronic reset of saidfocus-memory, constituting an erasure of said registered states offocus.
 7. The camera of claim 1, with an interval-selector contrivance,wherein means are arranged for selecting at least one operationalobject-distance interval, corresponding to the focusing interval withinwhich image detection is arranged to take place.
 8. The camera of claim7, and provided with an electronic image blur-function wherein means arearranged for defocusing image-parts outside said object-distanceintervals by using said blur-function, or replace said image parts withsome other picture.
 9. The camera of claim 1, wherein means are arrangedfor automatic setting of said differently-focused images, following aprogrammed, pre-selected scheme for focus-distances, the preferabledistribution of these being optimally even, from a depth offield-standpoint, and this constituting a set of standard focuses. 10.The camera of claim 1, and furnished with a proximity-selectorcontrivance, wherein means are allotted for setting the nearestfocus-distance allowed during image-detection, and this beingcontrollable with said proximity-selector, and said procedureconstituting an optional pre-selection.
 11. The camera of claim 1,having optimal-focus-selector and depth of field-selector contrivances,wherein means are arranged for selecting and focusing within the fieldof view with said focus-selector, on at least one object or distance ofpreference, for optimal image resolution and to furthermore set thedepth of field-selector for an object-distance interval of priority,within which depth of field-improvement is being arranged and this saidinterval being located in front of and/or behind said object/distance ofpreference.
 12. The camera of claim 1, and with more than oneimage-sensor, wherein means are arranged for electrical connection inbetween sensors in order to accomplish a common read-out.
 13. The cameraof claim 1, wherein said camera-objective comprises a permanentlyattached lens on the camera plus means being allotted for attachment ofa detachable afocal add-on lens with fixed or variable magnification.14. The camera of claim 1, wherein an image-sensor of the camera havingat least two mutually in parallel detector planes and that thesesurfaces are separated in order to register differently-focused images,one at each such plane.
 15. The camera of claim 1, wherein means areallocated for said selection extraction of image information by usingsaid image-sharpness detector and by utilizing a template- orimage-comparison technique, and where said image-registration forrespective final image and template image are independent, separaterecordings and at least one of the camera settings like exposure-time,aperture size, focal length and image sensor-sensitivity differ inbetween these two separate registrations.